NMR Tube Degradation Method for Sugar Analysis of Glycosides

A new cucurbitane - type triterpenoid from the bark of Elaeocarpus hygrophilus Kurz

A new cucurbitacin, 3β-(β-D-glucopyranosyloxy)-5β,6β:16α,23α-diepoxycucurbit-24-en-11-one or hygrocucurbin A (1), along with two known compounds, including 3β-(β-D-glucopyranosyloxy)-16α,23α-epoxycucurbita-5,24-dien-11-one (2) and (+)-lyoniresinol (3), were isolated from the bark of Elaeocarpus hygrophilus. Their chemical structures were elucidated by spectroscopic NMR, HR-IDA- TOF-MS analysis, and by comparison with the spectral data of corresponding compounds in the literature. Two cucurbitacins (1) and (2) were evaluated for their α-glucosidase inhibitory activity and cytotoxic against KB, MCF-7, Hep G2, and A549 cancer cell lines. For the α-glucosidase inhibitory activity, compound 1 showed an equivalent effect (IC50 197.4 ± 4.1 µM) compared to the acarbose, a positive control (IC50 208.5 ± 4.7 µM). And for the cytotoxicity, 2 was inactive while 1 was slightly sensitive against KB cells (IC50 233.3 ± 2.5 µM).

Spermacosides a and B, two new triterpenoid saponins from Spermacoce ocymoides burm.f

Two new triterpenoid saponins, named spermacosides A-B (1 - 2), together with two known oleanane-type triterpenoid saponins, 3-O-β-D-xylopyranosyl-(1→3)-β-D-glucopyranosylbayogenin (3) and 3-O-β-D-glucopyranosylbayogenin (4), were isolated from the ethyl acetate extract of Spermacoce ocymoides Burm.f. in a phytochemical investigation. Their chemical structures were elucidated by spectroscopic data analysis (1D and 2D NMR, and HR-ESI-MS), as well as comparison with reported data. All these compounds were evaluated for inhibiting nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 cells. Among them, 1 showed a slight effect with an IC50 value of 108.65 ± 7.91 µM, and compounds 2-4 were inactive.

Polysaccharides and Phenolic Compounds Recovered from Red Bell Pepper, Tomato and Basil By-Products Using a Green Extraction by Extractor Timatic®

Fruits and vegetables processing produces significant amounts of by-products rich in valuable bioactive compounds such as polyphenols and dietary fiber. Food by-product re-use promotes the eco-sustainability of several crops. This study aimed to apply green extractions of bioactive compounds from by-products of basil, tomato, and red bell pepper production. Tests were performed by applying extraction procedures both at laboratory scale and using the Timatic® extractor. Water and ethanol 10% and 20% were used for extraction of red bell pepper and tomato, testing different temperatures (30, 50, and 90 °C; water at 90 °C and ethanol 20% were applied for basil. The obtained phenolic extracts were analyzed by HPLC-DAD-MS. Polysaccharides of tomato and red bell pepper were extracted at laboratory scale and chemically characterized using 1H-NMR to define the methylation and acylation degree, and DLS to estimate the hydrodynamic volume. Laboratory extraction tests allowed efficient scaling-up of the process on the Timatic® extractor. Phenolic content in the dried extracts (DE) ranged 8.0-11.2 mg/g for tomato and red bell pepper and reached 240 mg/g for basil extracts. Polysaccharide yields (w/w on DM) reached 6.0 and 10.4% for dried tomato and red bell pepper, respectively. Dry extracts obtained using the Timatic® extractor and water can be useful sources of bioactive phenols. The study provided new data on tomato and red bell pepper polysaccharides that may be useful for future applications.

Cytotoxic triterpenoid saponins from the root of Olax subscorpioidea Oliv. (Olacaceae)

Bioactivity-guided phytochemical fractionation of the methanol extract of Olax subscorpioidea root has led to the isolation of six triterpenes. Three of these compounds are previously undescribed triterpenoid saponins: oleanolic acid 3-O-[α-L-rhamnopyranosyl-(1→3)-β-D-glucopyranosyl-(1 → 2)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (2), oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)-β-D-glucopyranoside] (3), and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside] ester (5). Other reported known compounds include two triterpene glycosides: oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (1) and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucuronopyranoside] (4); and a triterpene acid, oleanolic acid (6). The structures of these compounds were elucidated by spectroscopic means. The isolated compounds were tested against human cervical cancer (HeLa), colorectal cancer (Caco-2) and breast cancer (MCF-7) cell lines using the in vitro 3-[4,5-dimethylthiazole-2-yl] 3,5-diphenyltetrazolium bromide (MTT) assay, with vincristine as positive control. The cytotoxicity assay showed that compounds 3 and 5 exhibited significant inhibitory effects on the HeLa cell line, with IC50 values of 7.42 ± 0.34 μM and 10.27 ± 1.26 μM; and moderate effects on MCF-7 (IC50 values, 36.67 ± 1.23 μM and 43.83 ± 0.65 μM) and Caco-2 (IC50 values, 35.83 ± 0.55 μM and 39.03 ± 4.38 μM, respectively) cell lines. They were also more selectively cytotoxic than vincristine against the cancer cell lines, when compared with cytotoxicity against the normal lung cell line MRC5.

Primary Structure of Glycans by NMR Spectroscopy

Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a ¹H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.

A Pair of Chromone Epimers and an Acetophenone Glucoside from the Mangrove Endophytic Fungus Mycosphaerella sp. L3A1

Three new compounds, including a pair of chromone derivatives (1-2), and an acetophenone glucoside (3), together with three known compounds (4-6), were isolated from the mangrove endophytic fungus Mycosphaerella sp. L3A1. Their structures were elucidated by HR-ESI-MS analysis and extensive spectroscopic data. The absolute configurations of new compounds were determined using single-crystal X-ray diffraction analysis, electronic circular dichroism (ECD) calculations and chemical hydrolysis. In bioassays, compound 4 showed moderate cytotoxic activity against MDA-MB-435, HCT116, and SNB19 with IC₅₀ values in the range of 18.5-26.29 μM.

Phenolic compounds and polysaccharides in the date fruit (Phoenix dactylifera L.): Comparative study on five widely consumed Arabian varieties

The study analysed polysaccharides and phenolic compounds in widely consumed but little studied date fruits varieties such as Sukkari, Ajwa, Segae, Barrny and Khalas harvested at Tamr stage. The total phenols were in similar amount in the five varieties and ranged from 20 to 50 mg/100 g DW. The decoction and successive centrifugation made it possible to collect two main polysaccharide fractions for all the selected fruits. For each variety the first fraction was more abundant, with a lower swelling capacity and a higher amount of galacturonic acid (28.3% to 40.1%). The second fraction was only soluble in alkaline solution, with an average galacturonic acid content of only 17%. The different structure of the two polysaccharide fractions was also confirmed by the composition in neutral sugars and the degrees of methylation and acetylation. The proposed extraction procedure could be applied for larger scale extraction of the date fruit polysaccharides.

Discovery of varlaxins, new aeruginosin-type inhibitors of human trypsins

Low-molecular weight natural products display vast structural diversity and have played a key role in the development of novel therapeutics. Here we report the discovery of novel members of the aeruginosin family of natural products, which we named varlaxins. The chemical structures of varlaxins 1046A and 1022A were determined using a combination of mass spectrometry, analysis of one- and two-dimensional NMR spectra, and HPLC analysis of Marfey's derivatives. These analyses revealed that varlaxins 1046A and 1022A are composed of the following moieties: 2-O-methylglyceric acid 3-O-sulfate, isoleucine, 2-carboxy-6-hydroxyoctahydroindole (Choi), and a terminal arginine derivative. Varlaxins 1046A and 1022A differ in the cyclization of this arginine moiety. Interestingly, an unusual α-D-glucopyranose moiety derivatized with two 4-hydroxyphenylacetic acid residues was bound to Choi, a structure not previously reported for other members of the aeruginosin family. We sequenced the complete genome of Nostoc sp. UHCC 0870 and identified the putative 36 kb varlaxin biosynthetic gene cluster. Bioinformatics analysis confirmed that varlaxins belong to the aeruginosin family of natural products. Varlaxins 1046A and 1022A strongly inhibited the three human trypsin isoenzymes with IC₅₀ of 0.62-3.6 nM and 97-230 nM, respectively, including a prometastatic trypsin-3, which is a therapeutically relevant target in several types of cancer. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and provide evidence that the aeruginosin family is a source of strong inhibitors of human serine proteases.

Structure and Thermodynamics of Eu(III) and Cm(III) Complexes with Glucuronic Acid

Complexation by small organic ligands controls the bioavailability of contaminants and influences their mobility in the geosphere. We have studied the interactions of Cm³⁺, as a representative of the trivalent actinides, and Eu³⁺, as an inactive homologue, with glucuronic acid (GlcA) a simple sugar acid. Time-resolved laser-induced luminescence spectroscopy (TRLFS) shows that complexation at pH 5.0 occurs only at high ligand to metal ratios in the form of 1:1 complexes with standard formation constants log β⁰ = 1.84 ± 0.22 for Eu³⁺ and log β⁰ = 2.39 ± 0.19 for Cm³⁺. A combination of NMR, QMMM, and TRLFS reveals the structure of the complex to be a half-sandwich structure wherein the ligand binds through its carboxylic group, the ring oxygen, and a hydroxyl group in addition to five to six water molecules. Surprisingly, Y³⁺, which was used as a diamagnetic reference in NMR, prefers a different coordination geometry with bonding through at least two hydroxyl groups on the opposite side of a distorted GlcA molecule. QMMM simulations indicate that the differences in stability among Cm, Eu, and Y are related to ring strain induced by smaller cations. At higher pH a stronger complex was detected, most likely due to deprotonation of a coordinating OH group.

Acetylated Rhamnose Triterpenoid Saponins from Glechoma longituba Analyzed by LC-Q-TOFMS

The aim of the present work is to isolate a series of triterpene derivatives with rhamnosyl linking acetyl groups from Glechoma longituba according to the structural characteristics of previously described triterpene saponins. The extract ion chromatography spectrum of the crude extract of G. longituba was detected and analyzed by HPLC-HR-ESI-MS to determine possible components, and these metabolites were traced and separated by combining high-resolution mass spectrometry and predicted liquid chromatography retention time. Three 11α, 12α-epoxypentacyclic oleanolic acid triterpene saponins (glechomanosides H-J) and one ursane triterpene aldehyde saponin with a C-28 aldehyde group were isolated from G. longituba. The structure of these compounds was confirmed by NMR and compared with those of previously characterized compounds. The strategy described in this report enables a rapid, reliable, and complete analysis of glycoside compounds containing different numbers of acetyl groups at different positions on the sugar.

Detecting and Differentiating Monosaccharide Enantiomers by 1H NMR Spectroscopy

Monosaccharides play important roles in living organisms. They are present in essential glycoproteins, nucleic acids, and glycolipids as well as cell walls and bioactive natural product glycosides and polysaccharides. Monosaccharides are optically active, and as a routine, scientists make sure that their absolute configurations are determined when new natural glycosides are isolated. Many determination methods for the absolute configuration of monosaccharides have been reported, and thus far, taking advantage of their optical rotation differences is the most used and efficient method to distinguish enantiomers. This method, however, is not very convenient, because it requires a milligram amount of each pure sample and the availability of a polarimeter. Identification methods dealing with comparison of the retention times of the d- and l-diastereomeric monosaccharide derivatives by GC, TLC Rf values, HPLC, or UPLC have been also reported. Although effective, these methods still require sample preparation and a few milligrams of the test compounds. A new method with simple sample preparation to distinguish enantiomers of monosaccharides by analyzing the 1H NMR spectra of their diastereomeric derivatives has been developed. The monosaccharide components of a commercially available saponin-rich Panax ginseng and monoglycosides have been successfully identified using this procedure.

Optimizing acid hydrolysis for monosaccharide compositional analysis of Nostoc cf. linckia acidic exopolysaccharide

The exact estimation of monosaccharide composition is important in the primary structure elucidation of polysaccharides. An acid hydrolysis is usually performed for glycosidic bonds cleavage and releasing of monosaccharides. In this study, optimal conditions of total acid hydrolysis using trifluoroacetic acid (TFA) of acidic lactylated Nostoc cf. linckia exopolysaccharide (EPS) were investigated by NMR spectroscopy. Results of a series of experiments with modified acid concentration, temperature and time of hydrolysis, have shown 2 M TFA, 110 °C, 3 h as the most optimal. The stability of EPS monosaccharide components was also explored. Low stability was found at all tested conditions already during the first hour of hydrolysis; all neutral monosaccharides were degraded from 25% to 40% and glucuronic acid to 75%. NMR, contrary to standard techniques used in monosaccharide compositional analysis (HPLC, HPAEC), allowed simultaneous quantification of all GlcA forms; the free one, that one linked in oligosaccharides, as well as GlcA degradation product γ-lactone. NMR as detection method improves information about uronic acid content in EPS.

Five new cassane diterpenes from the seeds and bark of Erythrophleum suaveolens

Five new cassane-type diterpenoid heterosides, i. e. two cassane-type amides (1-2), two erythrophlamine-type amine esters (3-4) and a non‑nitrogenous erythrophlamine analogue (5) were isolated from the root barks (1-2) and the seeds (3-5) of Erythrophleum suaveolens. Their structures were unambiguously established by interpretation of their HRESIMS, 1D and 2D NMR data, and chemical degradation for sugar determination. Compounds 3-5 were evaluated for their cytotoxicity against a panel of three cell lines, revealing modest to strong activities.

A new triterpenoid saponin from Glinus oppositifolius

From the ethanol extract of Glinus oppositifolius, collected at Phu Yen province, Viet Nam, one new triterpenoid saponin (1) and four known compounds (2-5) were isolated. By means of NMR and HR-ESI-MS analyses, their structure was elucidated as 3-O-(β-D-xylopyranosyl-(1→3)-β-D-xylopyranosyl)spergulagenin A or glinusopposide V (1), glinusopposide L (2), spergulin B (3), vitexin (4) and astralagin (5). Two compounds (1-2) showed weak inhibitory activity against α-glucosidase.

Ene-yne Hydroquinones from a Marine-derived Strain of the Fungus Pestalotiopsis neglecta with Effects on Liver X Receptor Alpha

Seven unusual new ene-yne hydroquinones (1-3, 5-8), including three rare glycosylated derivatives named pestalotioquinosides A-C (6-8), were obtained from the marine-derived strain SCSIO41403 of the fungus Pestalotiopsis neglecta. Their structures including absolute configurations were elucidated by spectroscopic analysis and induced electronic circular dichroism experiments. In silico molecular docking and in vitro surface plasmon resonance studies showed that pestalotioquinoside C (8) could act as a liver X receptor alpha (LXRα) modulator. Further study showed that LXR target gene ABCA1 was significantly upregulated by 8, which revealed 8 as a potential LXRα agonist.

Chromogenic agents built around a multifunctional double-triazine framework for enzymatically triggered cross-linking under physiological conditions

A molecular architecture designed for bioconjugation and internal absorption ratiometry undergoes enzymatically triggered cleavage of glucosyl groups and subsequent oxidative dimerization in aqueous solution to yield indigoid-containing scaffolds.

A New Flavone Glycoside From Lumnitzera littorea with In Vitro α-Glucosidase Inhibitory Activity

A new flavone glycoside, lumnitzerone (1), was isolated from leaves of Lumnitzera littorea, together with 9 known flavonoids. Their structures were elucidated by spectroscopic (one-dimensional, two-dimensional nuclear magnetic resonance) and high-resolution mass spectrometry analysis, and comparison with literature data. Extracts and all isolated compounds were evaluated for α-glucosidase inhibitory activity; all the extracts and most of the isolated compounds exhibited better activities than the positive control acarbose.

Two new triterpenoids from the roots of Phyllanthus emblica

Two new triterpenes, the seco-friedelane type secofriedelanophyllemblicine and the ursane-derived saponin ursophyllemblicoside were isolated from the roots of the edible fruit-producing Phyllanthus emblica. Their structures were unambiguously elucidated using extensive 1D and 2D NMR analyses, high resolution mass spectrometry and single-crystal X-ray crystallographic analyses along with comparison with literature data. Secofriedelanophyllemblicine represents the first 3,4-secofriedelane bearing a carboxylic acid group substituent at C-20. Ursophyllemblicoside, incorporating the rare 21α hydroxyursolic acid as a sapogenol represents the first example of saponin comprising this aglycone. Secofriedelanophyllemblicine displayed a moderate cytotoxicity against K562 and HepG2 cancer cell lines.

MS/MS-Guided Isolation of Clarinoside, a New Anti-Inflammatory Pentalogin Derivative

Re-investigation of the chemical composition of the annual plant Mitracarpus scaber Zucc. led to the identification of clarinoside, a new pentalogin derivative containing a rare quinovose moiety, and the known compound harounoside. While the planar structure was fully determined using tandem mass spectrometry (MS) and quantum mechanics (QM) calculations, the tridimensional structure was unravelled after isolation and NMR analysis. The absolute configuration was assigned by comparison of experimental and theoretical synchrotron radiation circular dichroism spectra. Both compounds were tested for anti-inflammatory activity, and compound 1 showed the ability to inhibit the production of interleukin-8 (Il-8) with an IC50 value of 9.17 μM.

Akanthopyrones A-D, α-Pyrones Bearing a 4-O-Methyl-β-d-glucopyranose Moiety from the Spider-Associated Ascomycete Akanthomyces novoguineensis

Hypocrealean fungi have proved to be prolific bioactive metabolite producers; they have caught the attention of mycologists throughout the world. However, only a few studies on the insect and spider parasitic genus Akanthomyces have so far been carried out. In this study, we report the isolation, structural elucidation and biological activities of four unprecedented glycosylated α-pyrone derivatives, akanthopyrones A–D (1–4), from a culture of Akanthomyces novoguineensis collected in Thailand. The chemical structures of the akanthopyrones were determined by extensive 1D- and 2D-NMR, and HRMS spectroscopic analysis. Their absolute configurations were determined. Akanthopyrone A (1) exhibited weak antimicrobial activity against Bacillus subtilis DSM10 and cytotoxicity against the HeLa cell line KB-3-1, while akanthopyrone D (4) showed weak activity against Candida tenuis MUCL 29892.